The present invention relates to the manufacture of multi-layer capacitor or other electrical or electronic component chips.
Many electrical devices such as semiconductor chips, capacitors and the like are formed from multiple individual layers ("patterned substrates") of ceramic substrates on which is imprinted the desired electronic circuitry. The individual leaves are stacked together so that each layer of circuitry is sandwiched between two layers of insulating ceramic. The individual circuitry layers are then joined by electrical connections made either through holes in the ceramic substrates or by connections exterior to the laminated stack. (For brevity, these laminated electrical devices will often hereafter be referred to collectively as "capacitors." It will of course be understood, however, that the invention to be described is applicable to manufacture of all types of laminated electrical devices, not only capacitors. In addition, the patterned substrates and the "cover sheets" will often be referred to herein as "leaves".)
In practice, the individual capacitors are actually manufactured in the form of large wafers which contain dozens or hundreds of individual capacitors printed in a grid fashion. Once all the leaves have been stacked and laminated together, a wafer is sliced vertically so that each of the individual capacitors is separated from the wafer into a single device. Previously it has been common for such wafers to have dimensions of 3".times.4" (76.times.102 mm) or greater, with each of the individual capacitors having dimensions of 0.120".times.0.060" (3.0.times.1.5 mm; designated in the industry as a "1206" capacitor). Thus, a single laminated wafer might contain on the order of 1,000 individual capacitors which are subsequently sliced apart into individual devices.
In past practice, the individual leaves of printed ceramic substrates could be easily aligned and stacked together, since they had relatively large thicknesses, typically 1-3 mils (0.04-0.12 mm), and therefore were substantially rigid and easy to manipulate. However, recently two factors have arisen which have changed the situation dramatically. First, with the prior art thicker leaves, there was a tendency for air pockets to form between the layers caused by the raised printed electronic circuitry. As more leaves were added, the outer surfaces of the laminated stack tended to become irregular or wavy. The more leaves that were added (typically up to 30-50), the greater was the waviness, making registration of subsequent leaves in the manufacturing process that much more difficult.
Second, there has been a trend in the industry to require thinner and smaller laminated devices to increase capacity or conserve space. Much electrical and electronic equipment is designed to use laminated devices of specific external dimensions. Therefore, if the individual leaves can be made thinner, more leaves, and thus more capacity or complexity, can be incorporated into a laminated device while still maintaining the standard external device dimensions. Alternatively, in many cases there is a desire to have reduced external device dimensions, so that more devices can be incorporated into a piece of equipment without increasing the size of the piece of equipment or, with the same components, the piece of equipment itself can be made smaller. This is particularly important where the space in which the equipment is to be used is at a premium, such as in aircraft, spacecraft, satellites, computers, communication equipment and so forth. For instance, capacitor sizes have now been reduced to external dimensions such as 0.080".times.0.050" (2.0.times.1.3 mm; "0805" capacitors) and 0.040.times.0.020 in. (1.0.times.0.5 mm: "0402" capacitors), as well as other intermediate sizes. It is still important, however, to be able to obtain the same electrical or electronic capability in the thinner and smaller capacitors.
As these laminated devices have become smaller and thinner, the individual ceramic substrates have also become thinner so that the individual leaves have been much more difficult to bring into registry with the other leaves during manufacture. Tape as thin as 10 microns is now commonly used in manufacture of such components. The problem of registration and alignment has been sufficiently severe that production speeds have been substantially less than optimum so that overall yields of wafers have been reduced. In addition, because of the increasing problems with waviness, yields of the devices themselves have been further reduced by an increase in the numbers of unsatisfactory wafers which must be rejected. Since each wafer contains hundreds of individual devices, the loss of a single wafer represents a substantial reduction in the overall yield of the number of devices. Manual handling of thin wafers has also caused reduction in yields. As the tape (wafers) become even thinner, manual handling will not even be an option.
It would therefore be advantageous to have apparatus which could be used to bring the individual leaves quickly and accurately into registration for stacking. Such apparatus would be particularly desirable for use with thin leaves and where it could be fed by a continuous supply of such leaves substrates, could accurately and quickly align and register the individual leaves and stack them into an overall assembly of properly aligned leaves for subsequent bonding to form the unitary device.